1. Technical Field
The present invention relates to a temperature-sensitive automatic valve thermostat device used to control the temperature of cooling water in a cooling water circuit of an internal combustion engine (hereinafter “engine”) used in an automobile or the like that circulates the cooling water between the engine and a heat exchanger (hereinafter “radiator”) to cool the engine, in which the device operates on changes in the temperature of the cooling water to switch the flow of engine cooling water, and more particularly, to a thermo-element comprised of a thermal expansion unit that expands and contracts with changes in the temperature of the cooling water or other detected body and a moving member (a piston) moved by the expansion and contraction of the thermal expansion unit.
2. Description of the Background Art
In an automobile engine, for example, in order to cool the engine a water cooled-type cooling system using a radiator is generally employed. Conventionally, in this type of cooling system, a thermostat using a thermal expansion member or an electrically controlled valve unit that adjusts the volume of cooling water that is circulated to the radiator is employed in order to be able to control the temperature of the cooling water that is introduced into the engine.
In the above-described thermostat device using a thermal expansion member, a control valve is disposed at a portion of the cooling water route, for example, at the intake or the exhaust ends of the route. If the cooling water temperature is too low, the control valve is closed, causing the cooling water to circulate through a bypass route without passing through the radiator. If the cooling water temperature has become too high, the control valve is opened, causing the cooling water to flow through the radiator. As a result, the temperature of the cooling water is maintained in the required state.
Conventionally a variety of different structures for this type of thermostat device are known, having a first valve at one end of the thermo-element that operates by changes in the temperature of a fluid, a second valve at the other end of the thermo-element, biasing means that bias the first valve toward a closed position, and a frame.
The thermo-element consists of a temperature sensor and a guide. A thermal expansion unit of wax or the like that senses the temperature of the fluid and expands and contracts is built into the temperature sensor. A piston is fitted into the guide, which protrudes from the tip of the temperature sensor. A flange configured as a single integrated unit with the frame is provided at the tip of the piston to hold back the piston.
The first valve is poppet-shaped, and provided on the guide. The flange acts as the seat of the first valve. In addition, the flange has a mount projecting therefrom into the cooling water route.
The second valve is mounted on a rod projecting from the distal end of the temperature sensor. Between the second valve and the temperature sensor, the second valve is spring-biased toward the tip of the rod.
In this type of thermostat device, for example, the first valve is positioned to open and close the cooling water route and the second valve is positioned to open and close the bypass route. Then, the thermal expansion unit inside the temperature sensor expands as the temperature of the cooling water rises, pushing against the piston, and the thermo-element operates against the force of the biasing means. As a result, the first valve moves to the open position and opens the cooling water route while the second valve moves to the closed position and closes the bypass route. Conversely, the thermal expansion unit contracts as the temperature of the cooling water declines and the pressure on the piston thus weakens, moving the first valve to the closed position to close the cooling water route while the second valve moves to the open position to open the bypass route. (See, for example, patent documents JP-2004-177249-A and JP-2004-308743-A.)
However, in the thermo-element having the conventional structure described above, the element case is made of stainless steel material and internal parts of the element case are configured with a structure that directly pushes out the piston using a U-shaped packing as a seal. In addition, with such a thermo-element, in an effort to reduce the number of parts, the amount of expensive and high-specific-gravity metal alloys such as brass, and cost, where used in an automobile thermostat the product weight decreases, thus providing advantages such as the ability to achieve improved fuel efficiency. Moreover, unlike the conventional brass case, the element case made of stainless steel material has a wide area of elastic deformation, with the advantage that it can absorb even sudden, drastic changes in internal pressure.
However, with the thermo-element having the conventional structure described above, problems of machining and assembly arise during assembly of the thermo-element, leading to an increase in cost. Some sort of measure capable of solving such problems is sought.
For example, a guide member that slidably holds the piston is inserted inside the thermo-element case, while the first valve is mounted and fixed on the outside. When such a first valve is fitted onto the case and fixed thereat, if the external diameter of the case is interfered with prior to such fitting, then the seal member cannot maintain a seal due to deformation of the case, for example, leading to inadequate durability (reliability). Moreover, there is the problem of an adverse effect on assembly.